Welded Structural Member Corrosion Resistance in Sulfuric Acid
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Solution Overview
Problem
Austenitic stainless steel welding structure members experience bimetallic corrosion between the base material and weld metal, leading to corrosion issues in high-concentration sulfuric acid environments.
Innovation Solution
The composition of the base material and weld metal is optimized, with the base material containing 15.0 to 20.0% Cr, more than 3.0% Cu, and 2.0 to 5.0% Mo, and the weld metal having a Mo content of 6.0 to 17.0%, along with Co and/or Sn, to form stable passivation films and inhibit corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional austenitic stainless steel is used for welding structure members, then good hot workability is achieved, but bimetallic corrosion occurs between base material and weld metal in high-concentration sulfuric acid environments
Solution Approach 1:
The invention changes the chemical composition parameters of both base material and weld metal. Base material contains 15-20% Cr, 3-8% Cu, and 2-5% Mo, while weld metal contains 6-17% Mo and 0.1-0.6% Co. These parameter changes ensure both good hot workability and resistance to bimetallic corrosion in sulfuric acid environments.
Solution Approach 2:
The invention uses composite material strategy by optimizing the chemical composition of both base material and weld metal to create a matched system. The base material and weld metal form a composite structure where each component's composition is specifically designed to work together, preventing bimetallic corrosion while maintaining manufacturability.
2Use of energy by moving object
If the temperature of exhaust gas is lowered to or below the dew point of sulfuric acid to collect thermal energy, then energy efficiency is improved, but sulfuric acid dew point corrosion occurs
Solution Approach 1:
The invention changes the material composition parameters to enable operation at lower temperatures. By incorporating specific amounts of Cr, Cu, Mo, and Co in both base material and weld metal, the material can withstand sulfuric acid dew point conditions, allowing exhaust gas to be cooled to or below the dew point for maximum energy recovery without suffering from corrosion.
3Reliability
If Mo content in weld metal is increased to improve corrosion resistance, then bimetallic corrosion resistance is enhanced, but weld metal composition complexity increases
Solution Approach 1:
The invention optimizes the Mo content parameter in weld metal to be within 6-17%, which provides sufficient bimetallic corrosion resistance. Additionally, Co content is controlled at 0.1-0.6% to further enhance corrosion resistance. These parameter changes achieve the desired reliability while maintaining reasonable composition complexity through defined ranges rather than excessive elements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This composition significantly reduces bimetallic corrosion, enhancing the corrosion resistance of the welding structure member in environments with high-concentration sulfuric acid, ensuring optimal performance at temperatures from 50 to 100°C.
Implementation Method 1
the base material containing 15.0 to 20.0% Cr, more than 3.0% Cu, and 2.0 to 5.0% Mo, and the weld metal having a Mo content of 6.0 to 17.0%, along with Co and/or Sn, to form stable passivation films and inhibit corrosion
Data Source
AI summary
There is provided a welding structure member excellent in corrosion resistance in an environment where high-concentration sulfuric acid condenses, the welding structure member including base material having a chemical composition containing, in mass percent, C ≤ 0.05%, Si ≤ 1.0%, Mn ≤ 2.0%, P ≤ 0.04%, S ≤ 0.01%, Ni: 12.0 to 27.0%, Cr: 15.0% or more to less than 20.0%, Cu: more than 3.0% to 8.0% or less, Mo: more than 2.0% to 5.0% or less, Nb ≤ 1.0%, Ti ≤ 0.5%, Co ≤ 0.5%, Sn ≤ 0.1%, W ≤ 5.0%, Zr ≤ 1.0%, Al ≤ 0.5%, N < 0.05%, Ca ≤ 0.01%, B ≤ 0.01%, and REM ≤ 0.01%, with the balance: Fe and unavoidable impurities, and the welding structure member including including weld metal having a chemical composition containing, in mass percent, C ≤ 0.10%, Si ≤ 0.50%, Mn ≤ 3.5%, P ≤ 0.03%, S ≤ 0.03%, Cu ≤ 0.50%, Ni: 51.0 to 69.0%, Cr: 14.5 to 23.0%, Mo: 6.0 to 17.0%, Al ≤ 0.40%, Ti + Nb + Ta ≤ 4.90%, Co ≤ 2.5%, V ≤ 0.35%, and W ≤ 4.5%, with the balance: Fe and unavoidable impurities.